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  • 1. Al-Zoubi, N.
    et al.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Assessing the Exact Muffin-Tin Orbitals method for the Bain path of metals2017In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 97, no 15, p. 1243-1264Article in journal (Refereed)
    Abstract [en]

    We scrutinise the muffin-tin approximation and the screening within the framework of the Exact Muffin-Tin Orbitals method in the case of cubic and tetragonal crystal symmetries. Systematic total energy calculations are carried out for the Bain path including the body-centred cubic and face-centred cubic structures for a set of simple and transition metals. The present converged results in terms of potential sphere radius (S) and hard sphere radius (b) are in good agreement with previous theoretical calculations. We demonstrate that for all structures considered here, potential sphere radii around and slightly larger than the average Wigner–Seitz radius (w) yield accurate total energy results whereas S values smaller than w give large errors. It is shown that for converged total energies hard spheres with radii b = 0.7–0.8w should be used for an efficient screening within real space clusters consisting typically of 70–90 lattice sites. The less efficient convergence of the total energy in the case of small hard spheres is ascribed to the delocalisation of the screened spherical waves, which leads to inaccurate interstitial overlap matrix. The above conclusions are not significantly affected by the volume of the system.

  • 2. Bakaev, A.
    et al.
    Terentyev, D.
    Chang, Z.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Posselt, M.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Zhurkin, E. E.
    Effect of isotropic stress on dislocation bias factor in bcc iron: an atomistic study2018In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 98, no 1, p. 54-74Article in journal (Refereed)
    Abstract [en]

    The effect of externally applied stress on the dislocation bias factor (BF) in bcc iron has been studied using a combination of atomistic static calculations and finite element integration. Three kinds of dislocations were considered, namely, a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} edge and a0〈1 0 0〉{0 0 1} edge dislocations. The computations reveal that the isotropic crystal expansion leads to an increasing or constant dislocation bias, depending on the Burgers vector and type of dislocation. On the other hand, compressive stress reduces the dislocation bias for all the dislocations studied. Variation of the dislocation BF depending on dislocation type and Burgers vector is discussed by analysing the modification of the interaction energy landscape and the capture efficiency values for the vacancy and self-interstitial atom. 

  • 3.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    A possible mechanism of copper corrosion in anoxic water2012In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 92, no 36, p. 4618-4627Article in journal (Refereed)
    Abstract [en]

    Recent experiments show that solid Cu reacts with anoxic water. The reaction is observed by measuring the hydrogen release. This release is continuous and stable over a period of months. We have since theoretically found that water adsorbs dissociatively at a copper surface. But this adsorption is not enough to explain the amount of hydrogen released in the experiment. This observation calls for the explanation of the removal of the reaction product from the surface to provide a clean Cu surface where the water dissociation takes place. In this paper we investigate, by first-principles calculations, two possible mechanisms for this removal: first the possibility of Cu-O-H nanoparticulate formation, and second the diffusion of the dissociation products into Cu. We show that while the formation of nanoparticulates is energetically unfavorable, the diffusion of OH along grain boundaries can be substantial. The OH being placed in a grain boundary of the Cu sample quickly dissociates and O and H atoms diffuse independently of each other. Such a diffusion is markedly larger than the diffusion in bulk Cu. Thus, grain boundary diffusion is a viable mechanism for providing a clean Cu surface for the dissociation of water at the Cu surface. An order-of-magnitude estimate of the amount of hydrogen released in this case agrees with experiment. But this mechanism is not enough to explain the result of the experiment. We propose the formation of nanocrystals of copper oxide as a second step. A decisive experiment is proposed. 

  • 4. Bonny, G.
    et al.
    Castin, N.
    Domain, C.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Verreyken, B.
    Pascuet, M. I.
    Terentyev, D.
    Density functional theory-based cluster expansion to simulate thermal annealing in FeCrW alloys2017In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 97, no 5, p. 299-317Article in journal (Refereed)
    Abstract [en]

    In this work, we develop a rigid lattice cluster expansion as an ultimate goal to track the micro-structural evolution of Eurofer steel under neutron irradiation. The fact that all (defect) structures are mapped upon a rigid lattice allows a simplified computation and fitting procedure, thus enabling alloys of large chemical complexity to be modelled. As a first step towards the chemical complexity of Eurofer steels, we develop a cluster expansion (CE) for the FeCrW-vacancy system based on density functional theory (DFT) calculations in the dilute alloy limit. The DFT calculations suggest that only CrW clusters containing vacancies are stabilised. The cluster expansion was used to simulate thermal annealing in Fe–20Cr–xW alloys at 773 K. It is found that the addition of W to the alloy results in a non-linear decrease in the precipitation kinetics. The CE was found suitable to describe the energetics of the FeCrW-vacancy system in the Fe-rich limit.

  • 5.
    Dahlberg, Carl F. O.
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Gudmundsson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Hardening and softening mechanisms at decreasing microstructural length scales2008In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 88, no 30-32, p. 3513-3525Article in journal (Refereed)
    Abstract [en]

    A laminate structure with varying lamina thicknesses is used as a qualitative model of grain size dependence on yield behaviour in metallic materials. Both strain gradient plasticity and slip between layers are considered. It is shown that an inverse Hall-Petch effect can be generated in this way. For very small thicknesses, corresponding to very small grain sizes, sliding is the dominant mechanism and the strength then decreases with decreasing thickness. For larger thicknesses, strain gradient plasticity is controlling the deformation and the strength is, instead, increasing with decreasing thickness. Numerical examples are presented that demonstrate these mechanisms.

  • 6. Djurabekova, F.
    et al.
    Malerba, L.
    Pasianot, R. C.
    Olsson, Pär
    Dept. MMC, EDF-RD, Les Renardiéres, France.
    Nordlund, K.
    Kinetics versus thermodynamics in materials modeling: The case of the di-vacancy in iron2010In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 90, no 19, p. 2585-2595Article in journal (Refereed)
    Abstract [en]

    Monte Carlo models are widely used for the study of microstructural and microchemical evolution of materials under irradiation. However, they often link explicitly the relevant activation energies to the energy difference between local equilibrium states. We provide a simple example (di-vacancy migration in iron) in which a rigorous activation energy calculation, by means of both empirical interatomic potentials and density functional theory methods, clearly shows that such a link is not granted, revealing a migration mechanism that a thermodynamics-linked activation energy model cannot predict. Such a mechanism is, however, fully consistent with thermodynamics. This example emphasizes the importance of basing Monte Carlo methods on models where the activation energies are rigorously calculated, rather than deduced from widespread heuristic equations.

  • 7. Dupin, N.
    et al.
    Fries, S. G.
    Joubert, J. M.
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Sluiter, M. H. F.
    Kawazoe, Y.
    Pasturel, A.
    Using first-principles results to calculate finite-temperature thermodynamic properties of the Nb-Ni mu phase in the Bragg-Williams approximation2006In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 86, no 12, p. 1631-1641Article in journal (Refereed)
    Abstract [en]

    Results of first-principles (FP) total energy calculations for 32 different configurations of the mu phase in the binary system Nb-Ni are used in the compound energy formalism (CEF) to model finite-temperature thermodynamic properties. A comparison with Cluster Expansion Hamiltonian-Cluster Variation Method (CEH-CVM) calculations indicates that the CEF describes temperature-dependent site occupancies as well as the CEH-CVM within the temperature range of interest for applications. This suggests that the Bragg-Williams-Gorsky approximation (BWGA) used in the CEF is sufficient to describe site occupancies and thermodynamics of the mu phase. A phase diagram is calculated using the mu phase description derived in the present work together with a previous Calphad description for the other phases of this system. The FP-CEF approach significantly improves the description of the thermodynamic properties as a function of composition compared to the Calphad procedure generally used up to now.

  • 8.
    Forsblom, Mattias
    et al.
    KTH, Superseded Departments, Physics.
    Sandberg, Nils
    KTH, Superseded Departments, Physics.
    Grimvall, Göran
    KTH, Superseded Departments, Physics.
    Vibrational entropy of dislocations in Al2004In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 84, no 6, p. 521-532Article in journal (Refereed)
    Abstract [en]

    The region nearest to a lattice defect must be described by an atomistic model, while a continuum model suffices further away from the defect. We study such a separation into two regions for an edge dislocation. In particular we focus on the excess defect energy and vibrational entropy, when the dislocation core is described by a cluster of about 500-100 atoms, embedded in a large discrete and relaxed, but static, lattice. The interaction between the atoms is given by a potential of the embedded-atom model type referring to Al. The dynamic matrix of the vibrations in the cluster is fully diagonalized. The excess entropy DeltaS near the core has positive and negative contributions, depending on the sign of the local strain. Typically, DeltaS/k(B) approximate to 2 per atomic repeat length along the dislocation core in fcc Al. In the elastic continuum region far from the dislocation core the excess entropy shows the same logarithmic divergence as the elastic energy. Although the work refers to a specific material and defect type, the results are of a generic nature.

  • 9. Hepburn, D. J.
    et al.
    Ackland, G. J.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Rescaled potentials for transition metal solutes in α-iron2009In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 89, p. 3393-3411Article in journal (Refereed)
    Abstract [en]

    We present semi-empirical potentials for dilute transition metal solutes in α-iron. They are in the Finnis–Sinclair form and are therefore suitable for billion atom molecular dynamics simulations. The potentials have been developed using a rescaling technique to provide solute–iron and solute–solute interactions from an existing iron potential. By fitting to first principles calculations, which show clear trends in the properties of transition metal solutes in iron across the series, we find trends in the rescaling parameters, which we model using simple functions of the occupancy of the d-electron band. We comment on the possibility of utilizing such relationships for the fundamental electronic properties of the solute to create multicomponent potentials for transition metal solutes in α-iron.

  • 10.
    Johansson, Börje
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Sa
    Itinerant f-electron elements2009In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 89, no 22-24, p. 1793-1799Article in journal (Refereed)
    Abstract [en]

    To obtain a proper understanding of the 5f elements, the actinides, it is useful to compare their behavior with the 4f transition elements, the lanthanides. It is especially rewarding to capitalize on the remarkable similarity between the solid-state properties of compressed Ce and the actinide metals. The intensively studied alpha-gamma transition in Ce is considered to be a Mott transition, namely, the 4f electron changes its behavior from being localized to become delocalized (itinerant/metallic). This change also means that the 4f electron transforms from a non-bonding to a bonding configuration which, in turn, gives rise to a volume collapse. This collapse is isostructural in character, which contributes to the immense interest in this phase transition. An analogous and remarkable change in bonding (cohesive) properties is also found within the actinide series, where the sudden volume increase from Pu to Am (50%) can be viewed as a Mott transition within the 5f shell as a function of atomic number Z. The elements on the metallic side of the 5f Mott transition, i.e. the earlier actinides (Pa-Pu), show low symmetry structures at ambient conditions, while the heavier elements (from Am and beyond) adopt structures typical for the lighter trivalent lanthanide elements with localized 4f electrons. An important consequence of the localized and trivalent behavior in Am is a non-magnetic 5f(6) (J = L + S = 0) configuration for the f electrons. This led to the prediction of superconductivity in americium and subsequently to its experimental verification.

  • 11.
    Kádas, Krisztina
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Eriksson, O.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Theoretical prediction of the elastic properties of body-centered cubic Fe-Ni-Mg alloys under extreme conditions2012In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 92, no 7, p. 888-898Article in journal (Refereed)
    Abstract [en]

    Using density functional theory formulated within the framework of the exact muffin-tin orbital method, we investigate the elastic properties of the body-centered cubic Fe0.85Ni0.1Mg0.05 alloy in the conditions at the Earth's inner core. We demonstrate that in this system, the chemical stabilization effect of Mg is significantly larger than that of Ni. We show that the elastic properties of Fe(0.85)Ni(0.1)Mg(0.0)5 are in good agreement with those of the Earth's inner core, as given by seismic observations. We find that the excellent mechanical properties of Fe0.85Ni0.1Mg0.05 are primarily due to Mg.

  • 12.
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Modelling of sharp indentation experiments: some fundamental issues2006In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 86, no 33-35, p. 5155-5177Article in journal (Refereed)
    Abstract [en]

    Correct interpretation of sharp indentation experiments requires a fundamental understanding of the mechanics involved in the process. Such an understanding can only be achieved if an appropriate mechanical model is used to describe the problem. These models can, in rare cases, be purely analytical, but nowadays numerical modelling is a vital part of the mechanical approach. Furthermore, with the development of new materials and nanoindentation devices, material ( constitutive) modelling has becomes very important. The aim of the present paper is to present an overview of the modelling of sharp indentation experiments. Indentation of classical Mises elastoplastic behaviour, in particular, will be considered, in addition to indentation modelling of other types of materials. In addition, some fundamental issues in indentation modelling will be discussed. These issues include (1) the influence from large deformations, (2) differences and similarities between cone and pyramid indentation results, (3) the influence of residual stresses, (4) the effective elastic modulus at indentation and (5) the differences and similarities between indentation and scratch results. Most of these results have been published previously in international journals but their implications, in the author's opinion, have not been fully appreciated by the indentation community or, at least, not debated sufficiently.

  • 13. Lashley, Jason
    et al.
    Riseborough, Peter
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    A tribute to James L. Smith Foreword2009In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 89, no 22-24, p. 1751-1756Article in journal (Refereed)
  • 14.
    Li, Wei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Hu, Qing-Miao
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Kwon, Se Kyun
    Grehk, Mikael
    Johnsson, Jan Y.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden; Institute for Solid State Physics and Optics, Hungary.
    Generalized stacking fault energy of gamma-Fe2016In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 96, no 6, p. 524-541Article in journal (Refereed)
    Abstract [en]

    We investigate the generalized stacking fault energy ( [GRAPHICS] -surface) of paramagnetic [GRAPHICS] -Fe as a function of temperature. At static condition, the face-centred cubic (fcc) lattice is thermodynamically unstable with respect to the hexagonal close-packed lattice, resulting in a negative intrinsic stacking fault energy (ISF). However, the unstable stacking fault energy (USF), representing the energy barrier along the [GRAPHICS] -surface connecting the ideal fcc and the intrinsic stacking fault positions, is large and positive. The ISF is calculated to have a strong positive temperature coefficient, while the USF decreases monotonously with temperature. According to the recent plasticity theory, the overall effect of temperature is to move paramagnetic fcc Fe from the stacking fault formation regime ( [GRAPHICS] K) towards maximum twinning ( [GRAPHICS] K) and finally to a dominating full-slip regime ( [GRAPHICS] K). Our predictions are discussed in connection with the available experimental observations.

  • 15.
    Lundow, Per Håkan
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Markström, K.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    The Ising model for the bcc, fcc and diamond lattices: A comparison2009In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 89, no 22-24, p. 2009-2042Article in journal (Refereed)
    Abstract [en]

    A large-scale Monte Carlo simulation study of the Ising model for the simple cubic lattice was recently performed by us. In this paper, we complement that study with the bcc, fcc and diamond lattices. Both the canonical and microcanonical ensembles are employed. We give estimates of the critical temperature and also other quantities in the critical region. An analysis of the critical behaviour points to distinct high-and low-temperature exponents, especially for the specific heat, as was also obtained for the simple cubic lattice, although the agreement is good between the different lattices. The source of this discrepancy is briefly discussed.

  • 16.
    Lundow, Per Håkan
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    On the p, q-binomial distribution and the Ising model2010In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 90, no 24, p. 3313-3353Article in journal (Refereed)
    Abstract [en]

    We employ p, q-binomial coefficients, a generalisation of the binomial coefficients, to describe the magnetisation distributions of the Ising model. For the complete graph this distribution corresponds exactly to the limit case p = q. We apply our investigation to the simple d-dimensional lattices for d = 1, 2, 3, 4, 5 and fit p, q-binomial distributions to our data, some of which are exact but most are sampled. For d = 1 and d = 5, the magnetisation distributions are remarkably well-fitted by p,q-binomial distributions. For d = 4 we are only slightly less successful, while for d = 2, 3 we see some deviations (with exceptions!) between the p, q-binomial and the Ising distribution. However, at certain temperatures near Tc the statistical moments of the fitted distribution agree with the moments of the sampled data within the precision of sampling. We begin the paper by giving results of the behaviour of the p, q-distribution and its moment growth exponents given a certain parameterisation of p, q. Since the moment exponents are known for the Ising model (or at least approximately for d = 3) we can predict how p, q should behave and compare this to our measured p, q. The results speak in favour of the p, q-binomial distribution's correctness regarding its general behaviour in comparison to the Ising model. The full extent to which they correctly model the Ising distribution, however, is not settled.

  • 17.
    Lundow, Per Håkan
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    The p,q-binomial distribution applied to the 5d Ising model2013In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 93, no 14, p. 1755-1770Article in journal (Refereed)
    Abstract [en]

    The leading order form of the magnetization distribution is well-known for the 5d Ising model close to . Its corrections-to-scaling are not known though. Since we have earlier established that this distribution is extremely well-fitted by a -binomial distribution, we report considerably longer series expansions for its moments in terms of three parameters, providing new details on the scaling behaviour of the Ising distribution and its moments near . As applications, we give for example the scaling formulas for the ratios , and the full distribution at .

  • 18. Nurmi, E.
    et al.
    Tuuli, E.
    Levamaki, H.
    Kokko, K.
    Leiro, J.
    Vitos, Levante
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Directional Young's modulus of single-crystal and cold-rolled titanium from ab initio calculations: Preferred crystal orientation due to cold rolling2016In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 96, no 26, p. 2736-2751Article in journal (Refereed)
    Abstract [en]

    Titanium is a strong, corrosion resistant metal with low mass density, making it ideal for various purposes, including aviation and medical applications. In the present work, the elastic properties of titanium have been investigated using the first principles Exact Muffin-Tin Orbitals method. The focus of our study is the anisotropic elasticity of single-crystal and cold-rolled titanium. Both types of titanium are used in industrial applications because of their special mechanical properties compared to randomly ordered polycrystalline alloys. Single crystals have better creep resistance compared to polycrystalline metals, while cold-rolled ones, on the other hand, possess more strength. Here cold-rolled titanium is investigated for the first time using ab initio calculations. Single-crystal results are obtained directly from first principles total energy calculations, whereas the elasticity of the cold-rolled structure is estimated from the single-crystal data. The elasticity of cold-rolled titanium has previously been investigated only experimentally, and thus the present computational approach provides new insight and valuable complementary information, not only for cold-rolled titanium, but also for more complex structures. Our results are found to be in good agreement with experimental findings and therefore serve as a starting point for investigating the elasticity of titanium alloys, which, using our method, can be accomplished as easily as the pure titanium case.

  • 19. Nurmi, E.
    et al.
    Wang, G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kokko, K.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden; Wigner Research Centre for Physics, Hungary.
    Assessing the elastic properties and ductility of Fe-Cr-Al alloys from ab initio calculations2016In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 96, no 2, p. 122-133Article in journal (Refereed)
    Abstract [en]

    Fe-Al is one of the best corrosion resistant alloys at high temperatures. The flip side of Al addition to Fe is the deterioration of the mechanical properties. This problem can be solved by adding a suitable amount of third alloying component. In the present work, we use ab initio calculations based on density functional theory to study the elastic properties of Fe1-x-yCrxAly alloys for Al and Cr contents up to 20 at.%. We assess the ductility as a function of chemistry by making use of the semi-empirical correlations between the elastic parameters and mechanical properties. In particular, we derive the bulk modulus to shear modulus ratio and the Cauchy pressure and monitor their trends in terms of chemical composition. The present findings are contrasted with the previously established oxidation resistance of Fe-Cr-Al alloys.

  • 20. Punkkinen, M.P.J.
    et al.
    Hu, Q.-M.
    Kwon, S.K.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Kollar, J.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Surface properties of 3d transition metals2011In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 91, no 27, p. 3627-3640Article in journal (Refereed)
    Abstract [en]

    Using the projector augmented wave method within density functional theory, we present a systematic study of the layer relaxation, surface energy and surface stress of 3d transition metals. Comparing the calculated trends for the surface energy and stress with those obtained for 4d and 5d metals we find that magnetism has a significant effect on the surface properties. Enhanced surface magnetic moments decrease the size of the surface relaxation, lower the surface energy and surface stress, leading to compressive stress in Cr and Mn.

  • 21.
    Rahaman, Moshiour
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Razumovskiy, Vsevolod
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Temperature dependence of stacking-fault and anti-phase boundary energies in Al3Sc from ab initio calculations2013In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 93, no 25, p. 3423-3441Article in journal (Refereed)
    Abstract [en]

    Temperature dependence of intrinsic stacking-fault energies (SFE) and anti-phase boundary energies (APBE) of AlSc is investigated in first-principles calculations using the axial Ising model and supercell approach. The temperature effect has been taken into consideration by including the one-electron thermal excitations in the electronic structure calculations, and vibrational free energy in the harmonic approximation as well as by using temperature dependent lattice constant. The latter has been determined within the Debye-Gruneisen model, which reproduces well the experimental data. The APBE and SFE are found to be reduced by about 10% in the temperature interval from 0 to 1000 K. It is shown that the inclusion of the free energy of lattice vibrations in the harmonic approximation increases the SFE further by about 4%. We also find a substantial contribution from local lattice relaxations in the case of APBE for the (111) plane and SFE leading to their reduction by about 30%.

  • 22.
    Rapp, Östen
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Srinivas, V.
    Poon, S. J.
    Recent results at the metal-insulator transition of icosahedral AIPdRe2006In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 86, no 05-mar, p. 655-661Article in journal (Refereed)
    Abstract [en]

    The metal-insulator transition, MIT, in icosahedral AlPdRe has been studied from measurements of magnetoresistance and conductivity. Results for the localisation length xi, the characteristic hopping temperature To and their relations at the MIT are discussed. The results indicate important similarities between i-AlPdRe and doped semiconductors.

  • 23.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Single-site mean-field approach to thermal defects in binary ordered alloys2014In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 94, no 11, p. 1192-1201Article in journal (Refereed)
    Abstract [en]

    A single-site mean-field approach for the concentration of thermal defects in a binary intermetallic AB compound is proposed, which is a modification of previously existing Wagner-Schottky-type models. A numerical investigation of the model is done for the case of thermal defects in NiAl.

  • 24.
    Ruban, Andrei V.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Popov, V. A.
    Portnoi, V. K.
    Bogdanov, V. I.
    First-principles study of point defects in Ni3Al2014In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 94, no 1, p. 20-34Article in journal (Refereed)
    Abstract [en]

    The energetics and structural properties of native, substitutional and interstitial defects in Ni3Al have been investigated by first-principles methods. In particular, we have determined the formation energies of composition conserving defects and established that the so-called penta defect, which consists of four vacancies on Ni sublattice and Ni antisite on the Al sublattice, is the main source of vacancies in Ni3Al. We show that this is due to the strong Ni-site preference of vacancies in Ni3Al. We have also calculated the site substitution behaviour of Cu, Pd, Pt, Si, Ti, Cr, V, Nb, Ta and Mo and their effect on the concentration expansion coefficient. We show the latter information can used for an indirect estimate of the site substitution behaviour of the alloying elements. The solution energy of carbon and its effect on the lattice constant of Ni3Al have been obtained in the dilute limit in the first-principles calculations. We have also determined the chemical and strain-induced carbon-carbon interactions in the interstitial positions of Ni3Al. These interactions have been subsequently used in the statistical thermodynamic simulations of carbon ordering in Ni3Al.

  • 25.
    Thorning, Casper
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sridhar, Seetharaman
    Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh.
    Grain boundary ridge formation during initial high temperature oxidation of Mn/Al TRIP steel2007In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 87, no 23, p. 3479-3499Article in journal (Refereed)
    Abstract [en]

    Confocal scanning laser microscopy (CSLM) was used in real-time observation of alloy element oxidation of a Mn/Al TRIP steel in an Ar-O-2 atmosphere. CSLM images reveal a marked role of grain boundaries in the overall initial oxidation kinetics of the alloy, and consequently in the morphology of the initial surface oxide. The oxidation on the alloy surface is dominated by the formation of Mn-rich oxide ridges along grain boundary traces on the surface. Oxide ridge formation kinetics was quantified by measurements on images extracted from real-time recordings of surface oxide evolution. Oxide ridge growth was found to take place at a constant rate. Scanning electron microscopy (SEM) images of the oxidized surfaces showed homogenous oxide ridges along straight grain boundary traces and heterogeneous oxide ridges along non-straight grain boundary traces. A transport mechanism of Mn to the surface is proposed, which relies on grain boundary segregation of Mn and on a relationship between grain boundary diffusivity and grain boundary character. It is suggested that when regarding alloys with significant grain boundary segregation of a solute, separate Wagner balances for internal vs. external oxidation is required for the grain lattices and the grain boundaries, respectively.

  • 26.
    Xu, Zhihui
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    KTH, Superseded Departments, Metallurgy.
    An analysis of piling-up or sinking-in behaviour of elastic-plastic materials under a sharp indentation2004In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 84, no 23, p. 2367-2380Article in journal (Refereed)
    Abstract [en]

    Finite-element simulation has been carried out to investigate the piling-up or sinking-in behaviour of elastic - plastic strain-hardening materials under a sharp indentation. An empirical model is proposed to relate the contact area to the material parameter E/sigma(y) and the experimental parameter h(e)/h(max). Materials with E/sigma(y)

  • 27. Zolyomi, V.
    et al.
    Kollar, J.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    On the surface relaxation of transition metals2008In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 88, no 18-20, p. 2709-2714Article in journal (Refereed)
    Abstract [en]

    First principles band structure calculations are presented for the layer relaxation of the close-packed surfaces of 5d transition metals. Anomalously large relaxations are found for group IVA and VIIA hcp metals. For these elements, the size of the layer relaxation exhibits an unusually slow decay with the distance from the surface. We argue that this phenomenon can be attributed to the peculiar flat and degenerate d-bands located close to the Fermi level in the L-A-H top-plane of the hcp Brillouin zone, and which are also responsible for the anomalously low [001] longitudinal optical phonon frequencies observed in these hcp metals.

1 - 27 of 27
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